In many space temperature control situations, it is desirable to maintain different temperatures in different areas of the structure. It is usual to deal with this situation with so-called zone control. In this arrangement, a single HVAC unit provides heated or cooled air or heated water to each of the areas. The flow of the air or water to each area is under the control of a damper or valve operated by a thermostat dedicated to control of the temperature in that area.
While this is an extremely effective way to address the problem of maintaining different temperatures in different areas, it has disadvantages. The need for additional dampers or valves and additional thermostats adds cost. Where the zone control is added to an existing installation, the problem of adding the dampers or valves in existing ducts or pipes may be extremely expensive.
Another problem arises in single zone installations where it is necessary to control the temperature in different areas because of changing uses of the areas. For example, starting a fireplace in one's living room may increase the heat sensed by the nearby thermostat, causing the rest of the structure to be held uncomfortably cool. The same is true if a thermostat is located too close to the kitchen, when the oven is in heavy use. Of course, in these situations, it is possible to manually adjust the thermostat setting to compensate for the effect on its sensor, but the control is imprecise for other areas, with the result that comfort in those areas may be affected.
Accordingly, there is a need for a new approach in temperature control where different temperatures must be maintained in different areas of an enclosure.